1. Field of the Invention
The present invention relates to printing systems and, more particularly, is directed towards bar code printing systems.
2. Description of the Prior Art
High speed printing systems have been designed for use with electronic computers in the printing of alphanumerical characters and symbols on webs such as ticket blanks, labels and the like. One high speed printing system is the on-the-fly printer, which includes a rotating drum and ballistic elements. The print drum is provided with raised printing elements that are disposed about its periphery in arcuate columns, each printing element having a unique address location. A document to be printed is fed into a print gate disposed between the drum and ballistic elements. In response to coded signals representing a particular character to be printed, the ballistic elements are actuated for urging the document against the printing elements on the print drum. The coded signals define a particular address on the drum at which the character to be printed is located.
Although high resolution is desirable, it is not critical unless the printed characters are machine readable bar codes. Reliable reading of bar code indicia is realized if the bar imprints are well defined with good contrast and there are no unprinted areas. The readable quality of the bar imprint depends upon how well the printing elements are inked. Generally, the print drum of the on-the-fly printer is inked by an ink roller that presses against the drum as it rotates. If the drum makes several revolutions in contact with the ink roller before the bar printing element is used, the quality of the resulting bar code imprint is high. Such printers suffer from the disadvantage of long printing times. If the drum makes only one revolution in contact with the ink roller before the bar printing element is used, the bar code imprint is light and may contain unprinted area within its boundaries. Such printing systems suffer from the disadvantage of limited reliability in the reading of the bar code messages.